1. Field of the Invention
This invention relates generally to image processing systems, and more particularly, to an image processing system for analyzing contrast and spatial frequency features in order to identify an image.
2. Description of the Prior Art
Image identifying systems are known. Such systems range from feature following systems that analyze the contour of a particular feature to systems that detect the gross features of a document, such as size, color, luminescence, density and spectroscopic features. While such systems provide a way to identify images, the feature following systems are orientation dependent, and as such, require either proper orientation of the image, or orientation compensating circuitry. The requirement for proper orientation or orientation compensating circuitry reduces the speed with which a document can be read, and the accuracy of identification is substantially reduced when proper orientation or orientation compensation circuitry is not used.
Systems utilizing gross feature analysis for identification do not require proper orientation or orientation compensating circuitry; however, no single gross feature provides sufficient information to distinguish a particular image from more than a relatively small number of images. Thus, in order to distinguish a particular image from a relatively large number of images, several gross features must be analyzed. The analysis of several gross features may be done in cascade with, for example, size, luminescense, reflectivity, and color features being serially analyzed to identify a coupon, as described in copending U.S. patent application Ser. No. 872,359, filed on Jan. 26, 1978 by the present inventor. The aforesaid application issued as U.S. Pat. No. 4,166,540 on Sept. 4, 1979. Such serial analysis increases the accuracy of identification, and identification may be made before all of the gross characteristics are analyzed; however, such systems are relatively expensive because they require a separate analyzer for each gross characteristic being analyzed. Moreover, when a large number of images are processed, more characteristics must be analyzed, and the number of analyzers must be further increased. This further increases the cost of the system, both in terms of the number of analyzers that must be employed and the cost of the computer system required to analyze the results of a large number of analyses.